Boolean intersect with plane makes object disappear
First. The scale of your plane is set to negative.



Press CtrlA in object mode and select apply scale.

Then the river object has inverted normals. 



Make them consistent by pressing ctrl N



Booleans use the direction of the normals to calculate the operation.

Then use Difference to cut out the shape of the river out of the plane:



Some reasons for failed booleans operations: 


Non-Manifold geometry
Inconsistent normals
Booleans don't work with curves or text
The scale for the object uses negative values